JPH0789493B2 - Fuel system controller for fuel cell power plant - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a fuel system control device for a fuel cell (hereinafter referred to as FC) power generation plant, and more particularly, to a hydrocarbon reformer in a fuel reformer. The raw fuel containing the main component is reacted with water to reform it into the fuel gas containing hydrogen as the main component, and this fuel gas is supplied to the fuel cell as a reducing agent and the fuel exhaust gas discharged from the fuel cell is reformed. The present invention relates to a control device that can always maintain a stable reformer temperature in a fuel system that is burned as a heat source necessary for reforming the fuel.

[Technical background of the invention and its problems]

As is well known, an FC power plant includes a power section that generates electric power, a fuel system that produces hydrogen-rich fuel gas and supplies it to FC, an air system that pressurizes air to supply FC, and an FC It consists of a thermal management system that controls the temperature.

By the way, as shown in FIG. 7, the fuel system of an FC power plant is usually composed of a reformer 1 that converts steam into a hydrogen-rich fuel gas by adding steam to a raw fuel gas mainly containing hydrocarbons. It is composed of a shift converter 2 for generating hydrogen by adding steam to the generated carbon monoxide. Since the reforming reaction for converting hydrocarbons into hydrogen is an endothermic reaction, the fuel gas (hereinafter, referred to as FC fuel exhaust gas) after passing through FC4 through the flow control valve 3 is usually used as a reformer burner. Guide to 5, this FC
The amount of heat necessary for the reaction in the reformer 1 is obtained by burning the hydrogen in the fuel exhaust gas. Further, the temperature control of the reformer 1 is performed by adjusting the flow control valve 3.

However, the conventional fuel system configured as described above has the following problems. That is, it takes a long time for the temperature of the reformer 1 to stabilize after operating the flow control valve 3, and even if the flow rate of the fuel gas is the same, the combustion energy is changed by the hydrogen concentration and the residual hydrocarbon concentration in the FC fuel exhaust gas. Because of the large difference, it was very difficult to control the temperature of the reformer 1 to be constant. As an example, when the load current of FC4 is changed, as shown in Fig. 8 and Fig. 9, the reformer reaction tube temperature fluctuates greatly and it is not easy to settle it. Such vibration not only causes unnecessary thermal fatigue to the reformer reaction tube and shortens its life, but also makes the reforming reaction rate unstable and hinders the supply of fuel gas to the FC4, making it difficult to achieve a fast load response. Was there.

[Object of the Invention]

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a fuel cell capable of promptly making a fuel gas flow rate follow a target value while always maintaining a constant reformer reaction tube temperature. It is to provide a fuel system control device for a power generation plant.

[Outline of Invention]

The control device according to the present invention causes a reformer to react water with a raw fuel containing hydrocarbon as a main component to reform it into a fuel gas containing hydrogen as a main component, and supplies this fuel gas as a reducing agent to a fuel cell. At the same time, a fuel system of a fuel cell power plant in which the fuel exhaust gas discharged from the fuel cell is burned as a heat source necessary for reforming in the reformer is a control target. In order to control such a system, the control device according to the present invention includes a reformer main burner that burns fuel exhaust gas discharged from a fuel cell in a reformer, a reformer auxiliary burner connected to a fuel supply source, and a reformer auxiliary burner. Means for calculating correction energy for maintaining the temperature of the reformer reaction tube at the target temperature from the difference between the target temperature of the reformer reaction tube and the actual temperature, and the reforming rate of the reformer from the temperature of the reformer reaction tube. And means for calculating the combustion energy of the fuel exhaust gas supplied to the reformer main burner from the means for obtaining, the reforming rate obtained by this means, the load current of the fuel cell, and the flow rate of the fuel gas supplied to the fuel cell. Means, a flow rate of the raw fuel flowing into the reformer, and a combustion exhaust gas flow rate discharged from the reformer, Means for calculating the energy consumption in the reformer from the temperature and the reforming rate, means for obtaining the balance energy in the reformer from the difference between the combustion energy and the consumption energy, and the difference between the correction energy and the balance energy. And means for controlling the amount of fuel supplied to the reformer auxiliary burner.

〔The invention's effect〕

With the above configuration, the heat balance of the reformer is always calculated, and the fuel supply amount to the reformer auxiliary burner is controlled corresponding to it, so that it is stable without being affected by the component change of the FC fuel exhaust gas. The reformer temperature can be controlled, and the reformer temperature control can be significantly facilitated. In addition, because the reformer auxiliary burner is installed in the reformer combustion chamber as the control end of the reformer temperature, the operation end is operated unlike the conventional one that is controlled by the valve installed on the upstream side of the FC. The time from when the temperature changes to the temperature can be shortened. Therefore, quick follow-up performance and high disturbance suppression performance can be realized.

Example of Invention

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a main part of a fuel cell power plant incorporating a control device according to an embodiment of the present invention.

That is, in the figure, 11 indicates the feed end of raw fuel containing hydrocarbons as the main component, and 12 indicates the feed end of steam. The raw fuel and steam supplied to the supply ends 11 and 12 are connected to the pipes 13 and 14, respectively.
After being introduced and merged with each other, they are introduced into the reformer reaction tube 16 of the reformer 15 and reformed into a fuel gas containing hydrogen as a main component. The fuel gas sent from the reformer reaction tube 16 is sent to the FC 18 as a reducing agent via a shift converter (not shown) and a flow control valve 17. And FC18
The fuel exhaust gas discharged from is supplied to the reformer main burner 20 via the pipe 19. On the other hand, a part of the raw fuel supplied to the supply end 11 is supplied to the reformer auxiliary burner 23 via the pipe 21 and the flow control valve 22.

In the figure, 24 is a flow meter for measuring the flow rate of the fuel gas supplied to the FC 18, 25 is a flow meter for measuring the flow rate of the raw fuel flowing into the reformer reaction tube 16, and 26 is a flow meter.
Is a flow meter for measuring the combustion exhaust gas flow rate of the reformer 15, 27 is a flow meter for measuring the flow rate of the raw fuel supplied to the reformer auxiliary burner 23, and 28 is the temperature of the reformer reaction tube 16. 29 shows a thermometer for measuring the temperature of the combustion exhaust gas. Reference numeral 30 in the figure denotes a fuel flow rate calculator for calculating a fuel flow rate corresponding to the load request command LP and outputting a fuel flow rate signal as shown in FIG.
The output of 30 is given to the controller 31. controller
31 is a flow signal F ₁ obtained by the output of the calculator 30 and the flow meter 24.
And is configured to control the opening of the flow control valve 17 so that the flow rate signal F ₁ matches the output of the calculator 30.
In the figure, 32 indicates a controller.
32 compares the output M of the auxiliary burner output calculator 33 to be described later with the flow signal F ₄ obtained in the flow meter 27, the opening degree of the flow regulation valve 22 so that the flow rate signal F ₄ matches the output M It is configured to control.

Therefore, the flow rate signals F ₁ , F ₂ , F ₃ obtained by the flow meters 24, 25, 26
The temperature signals T ₁ and T ₂ obtained by the thermometers 28 and 29 are introduced into the auxiliary burner output calculator 33. The auxiliary burner output calculator 33 is for calculating the heat balance of the reformer 15 and controlling the fuel supply amount to the reformer auxiliary burner 23 in consideration of the excess and deficiency of the balance. It is configured as shown in the figure. That is, the main part of the calculator 33 is roughly divided into a correction energy calculator 34, a heat balance calculator 35, a burner output calculator 36 for estimating the output of the reformer main burner 20, and a reforming ratio calculator 37. And a divider 38.

The correction energy calculator 34 introduces a difference signal between the target temperature signal RTT of the reformer reaction tube 16 and the actual temperature signal T ₁ obtained by the thermometer 28 through the subtractor 39 to perform PI calculation,
This is for calculating the correction energy for maintaining the reformer reaction tube 16 at the target temperature. Then, the correction energy signal G produced by the correction energy calculator 34
Is introduced into one input terminal of the subtractor 40.

The reforming rate calculator 37 calculates the progress rate of the reaction shown by the following equation (1), which proceeds in the reformer 15 and the shift converter, from the temperature of the reformer reaction tube 16, that is, the temperature signal T ₁ obtained from the thermometer 28. It is for estimation.

CH ₄ + 2H ₂ O → 4H ₂ + CO ₂ (1) The rate of progress of this reaction, that is, the reforming rate, actually depends on the pressure and the flow rate of the raw fuel (the above formula is methane) in addition to the temperature. However, in an FC power plant, conditions other than temperature can be considered to be almost constant, and as shown in Fig. 4, the higher the temperature, the closer the reforming rate approaches 1. Therefore, in this embodiment, the reforming rate is calculated based on the temperature signal T ₁ .

The burner output calculator 36 is for estimating the combustion energy in the reformer main burner 20 using the reforming rate x calculated by the reforming rate calculator 37. That is, this computing unit 36
Is the FC fuel flowing into the reformer main burner 20 using the following equations (2) and (3) by introducing the flow rate signal F ₁ of the flow meter 24, the reforming rate x, and the load current signal Load. Exhaust gas flow rate F _EX
And its energy density E _EX are calculated, and the combustion energy is calculated from this.

F _EX ＝ Fand−k ₁ × Load… (2) E _EX ＝ k ₂ (A ・ k ₃・ Fand−k ₄・ E _H2・ Load) / F _EX … (3)
However, F _EX ; FC fuel exhaust gas flow rate (kgmol / hr) E _EX ; FC fuel exhaust gas combustion energy per unit volume (kcal / k
gmol) Fand; Fuel gas flow rate detected by flow meter 24 (kgmol / hr) Load; FC load current (A) A; C / DC; (1-x) E _CH4 + 4xE _H2 D; 1 + 4x E _CH4 ; CH ₄ combustion energy (= 221.8kcal / mol, 1atm25 ℃ ) of E _H2; H ₂ combustion energy (= 57.8kcal / mol, 1atm25 ℃ ) x; modification rate k ₁ to k _4; constant in this way, F _EX And the combustion energy signal E obtained by the product of E _EX is introduced into the heat balance calculator 35.

The heat balance calculator 35 includes a combustion energy signal E, a raw fuel flow rate signal F ₂ , an exhaust gas flow rate signal F _3, and an exhaust gas temperature signal T ₂
And the reforming rate x are introduced, and the heat balance in the reformer 15 is calculated using the following equations (4) to (7).

Qb = Q _F -Q _EX -Q _RF (4) Q _F = F _EX / E _EX ... (5) Q _EX = k ₅ · F ₀ · T ₅ ... (6) Q _RF = E _RF · F _I · x… (7) However, Qb; Heat balance (kcal / hr) Q _F ; Reformer main burner output (kcal / hr) Q _EX ; Exhaust gas heat removal amount (kcal / hr) Q _RF ; Reformed gas heat absorption amount (kcal) / hr) F ₀ ; Exhaust gas flow rate (kgmol / hr) T ₀ ; Exhaust gas temperature (℃) E _RF ; Endotherm due to reforming reaction (kcal / .kgmol) F _I ; Raw fuel supply (kgmol / hr) k ₅ ; Constant (kcal / kgmol · ° C.) In this way, the heat balance signal H obtained by the heat balance calculator 35 is introduced to the other input terminal of the subtractor 40. And
The output of the subtractor 40 is introduced into the divider 38. The divider 38 outputs a signal M obtained by dividing the output signal Y of the subtractor 40 by a unit flow rate of the raw fuel which is known in advance and the fuel energy J. And this signal M is the controller
It is given to 32 as a flow control signal. Therefore, the reformer auxiliary burner 23 is always supplied with an amount of fuel necessary for maintaining the temperature of the reformer reaction tube 16 constant.

As described above, the reformer auxiliary burner 23 is provided, the heat balance of the reformer 15 is obtained, and the fuel supply amount to the reformer auxiliary burner 23 is controlled in consideration of this heat balance. As a result, the fuel system can respond quickly to sudden load demands, and the reformer 15
It is possible to slightly suppress the temperature fluctuations. Figure 5 shows
This figure shows a state of actual control using this control device. As can be seen from this figure, a fast fuel flow response can be realized. Further, since the temperature of the reformer reaction tube 16 can be stabilized, thermal fatigue of the reformer reaction tube 16 can be prevented, and the life can be greatly extended, so that the above-mentioned effects can be finally exhibited. .

FIG. 6 is a block diagram showing another embodiment of the present invention.

In the figure, 101 is a reformer, which introduces methane as a raw fuel mixed with water vapor into the reformer reaction tube inside which a reforming catalyst layer is installed, and burns fuel outside the reformer reaction tube. Main burner 107 and auxiliary reformer burner for combustion chamber
By passing the high-temperature combustion gas obtained by combustion at 108, a reformed gas containing a large amount of hydrogen is generated. Further, 103 is a transformer having the same function as described above, 104 is the gas obtained by the transformer 103 is introduced as a fuel gas into the fuel electrode, and an oxidant gas such as air is introduced into the oxidant electrode. It is a fuel cell that extracts electrical energy from between both electrodes by an electrochemical reaction that occurs. The fuel gas discharged from the fuel electrode of the fuel cell 104 is supplied to the main reformer burner 107 in the combustion chamber of the reformer 101, and methane is supplied as fuel gas separately supplied from the outside to the reform auxiliary burner 108. , Each of them is introduced as the fuel for combustion.

On the other hand, 109 is a flow rate control valve provided on the line for supplying the fuel gas to the reformer auxiliary burner 108, 110A is provided on the line through which methane, which is the raw fuel, flows, and the first flow rate detection for detecting the flow rate is provided. A second flow rate detector 110B is provided on the line through which methane mixed with water vapor flows and detects the flow rate thereof. A second flow rate detector 110C is provided on the line immediately after the outlet of the reformer 101 to detect the flow rate. The third flow rate detector 110D is provided on the line for supplying the fuel gas to the reformer auxiliary burner 108, and the fourth flow rate detector 111 detects the flow rate of the fuel gas. It is a current detector as an output electric quantity detector for detection. Further, 112 is each of the above flow rate detectors 110A to 110D
And detection signals F _A to F output from the current detector 111, respectively.
First, the amount of combustion energy Q in the combustion chamber of the reformer 101 in which the composition change of the fuel gas is taken into consideration based on the scientific knowledge such as the reforming reaction and the combustion reaction using _D and I as inputs 1 Arithmetic unit, 113 is the current detector 11
The combustion energy amount corresponding to the detection signal I output from 1 is compared with the combustion energy amount Q calculated by the first arithmetic unit 112, and the valve of the flow rate control valve 109 is based on the comparison effect. It is the 2nd arithmetic unit which outputs the control signal Vc which adjusts an opening.

Here, the first arithmetic unit 112 includes an adder / subtractor 114 and an adder / subtractor 11
5, adder / subtractor 116, adder / subtractor 117, adder / subtractor 118, coefficient unit 119, coefficient unit 120, coefficient unit 121, coefficient unit 122, coefficient unit 123A, coefficient unit 123B,
The second arithmetic unit 113 is configured from the coefficient unit 124 as shown in the figure, and the second arithmetic unit 113 includes a function generator 125, a limiter 126, a coefficient unit 127, and an adder / subtractor 1
It is constructed as shown in FIG.

Next, the combustion control action of the combustion chamber of the reformer 101 in the fuel cell power generation system configured as described above will be described.

First, the fuel reforming reaction in the reformer 101 can be generally regarded as the chemical reaction represented by the above formula (1). Although this reaction is a reversible reaction, the movement of the equilibrium point to the right can be known as a change in the molar flow rate of the reaction flow rate. Ie. 1
An increment of 2 moles of fuel gas occurs for the reaction of moles of methane. From this, it can be seen that half of the difference in the flow rate of the fuel gas before and after the reforming reaction is equal to the flow rate of methane that caused the reforming reaction.

Now, the first flow rate detector 110A, the second flow rate detector 110B, the third
Of the flow signal which are respectively detected by the flow detector 110C F _A, F _B,
If it is F _C , the methane flow rate F _R reacts and the first arithmetic unit 11
Subtractor 114 in 2, the coefficient unit 119, F _R = a _{(F C -F B) / 2} ...... (8).

On the other hand, the hydrogen flow rate F _H generated by the reforming reaction and
The methane flow rate F _M remaining after the reforming reaction is calculated by the coefficient unit 120,
With the adder / subtractor 115, F _H = 4 · F _R (9) F _M = F _A −F _R (10) Therefore, the energy flow rate as the combustible component of the fuel gas after the reforming reaction becomes Q ₁ · F _M + Q ₂ · F _H (11) by the coefficient unit 121, the coefficient unit 122, and the adder / subtractor 116. Here, Q ₁ and Q ₂ are the combustion heat of methane and hydrogen, respectively. Then, this passes through the fuel cell 104 with an appropriate transmission delay (coefficient multiplier 123A). On the other hand, the flow rate of hydrogen consumed in the fuel cell 104 is equal to the output current I of the fuel cell 104, which is determined by multiplying the detection signal from the current detector 111 by the physical constant in the coefficient unit 124. can do. Further, the combustion gas energy obtained by subtracting the hydrogen energy consumed by the fuel cell 104 by the adder / subtractor 117 is further converted into combustion heat by the reformer main burner 107 with a further transmission delay (coefficient unit 123B). . Then, by adding the detection signal F _D from the fourth flow rate detector 110D to the adder / subtractor 118, the heat quantity Q generated by the reformer auxiliary burner 108 is calculated.

On the other hand, in the second arithmetic unit 113, the combustion energy amount corresponding to the detection signal I from the current detector 111 is obtained by the function generator 125 as Qref, and this value Qref is used as the target value to perform the first arithmetic operation. A deviation signal from the combustion energy amount Q calculated by the device 112 is obtained by the adder / subtractor 128, which is converted into a control signal Vc through the second arithmetic device 113 and the counter 127 and is given to the flow control valve 109. The flow rate of methane, which is the fuel gas supplied to the flow control valve 109, is controlled.

The present invention is not limited to the above embodiment. For example, the auxiliary burner output calculator may be realized as software on a computer. In addition,
Of course, various modifications can be made without departing from the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram of a fuel cell power plant incorporating a control device according to an embodiment of the present invention, FIG. 2 is a diagram showing an output characteristic of a fuel flow rate calculator in the plant, and FIG.
Fig. 4 is a block diagram of an auxiliary burner output computing unit in the plant, Fig. 4 is a diagram for explaining the relationship between reformer reaction tube temperature and reforming rate, and Fig. 5 is a condition using the control device according to the present invention. The figure which shows the change of each process quantity when load current is changed under, Figure 6 is the principal part block diagram of the fuel cell power plant which incorporates the control device which relates to the other execution example of this invention, 7th FIG. 8 is a configuration diagram of a conventional fuel system, and FIGS. 8 and 9 are diagrams for explaining problems of the conventional system. 11 …… Raw fuel supply end, 12 …… Steam supply end, 15, 101…
… Reformer, 16 …… Reformer reaction tube, 17,22 …… Flow control valve, 18,104 …… Fuel cell (FC), 20,107 …… Reformer main burner, 23,108 …… Reformer auxiliary burner, 30 …… Fuel flow rate calculator, 31,32 …… Controller, 33 …… Auxiliary burner output calculator, 34 …… Correction energy calculator, 35 …… Heat balance calculator, 36 …… Burner output calculator, 37 …… Reformation ratio calculator, 38 …
... Divider, 112 ... First arithmetic unit, 113 ... Second arithmetic unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Reiji Mitarai Reiji Mitarai No. 1 Toshiba-cho, Fuchu-shi, Tokyo Inside the Fuchu factory, Toshiba Corp. (56) Reference JP-A-58-166675 (JP, A)

Claims (2)

[Claims] 1. A reformer causes water to react with a raw fuel containing hydrocarbon as a main component to reform it into a fuel gas containing hydrogen as a main component, and this fuel gas is supplied to a fuel cell as a reducing agent and the fuel is also used. A fuel system for controlling a fuel system of a fuel cell power plant, which burns fuel exhaust gas discharged from a cell as a heat source necessary for reforming in the reformer, the fuel discharged from the fuel cell The reformer main burner that burns exhaust gas in the reformer, the reformer auxiliary burner connected to the fuel supply source, and the difference between the target temperature of the reformer reaction tube and the actual temperature keep the temperature of the reformer reaction tube at the target temperature. For calculating the correction energy for calculating the reforming rate of the reformer from the temperature of the reformer reaction tube Means for calculating the combustion energy of the fuel exhaust gas supplied to the reformer main burner from the reforming rate, the load current of the fuel cell and the flow rate of the fuel gas supplied to the fuel cell, and the means for flowing into the reformer. Means for calculating energy consumption in the reformer from the flow rate of the raw fuel, the flow rate of combustion exhaust gas discharged from the reformer, its temperature, and the reforming ratio, and balance energy in the reformer from the difference between the combustion energy and the consumption energy. And a means for controlling the fuel supply amount to the reformer auxiliary burner in correspondence with the difference between the corrected energy and the balance energy, and a fuel system for a fuel cell power plant. Control device. 2. The fuel system for a fuel cell power plant according to claim 1, wherein the fuel supply source to which the reformer auxiliary burner is connected is the same as the raw fuel supply source. Control device.